Gymnosperms and angiosperms share a common ancestor around 300 MYA and the genetic system for the specification of gymnosperm and angiosperm reproductive organ identity was more than likely from a functionally related system in the common ancestor to all seed plants. In angiosperms floral organ identity is primarily determined by interactions of five type II MADS box genes (ABCDE) and clear homologs of the A/E, B and C/D lineages are found in gymnosperms. Particularly interesting in the evolution of seed plant reproductive structure are B-class genes. In both angiosperms and gymnosperms, B-like gene expression is associated with male reproductive structures, the stamens and male cones respectively. Angiosperm and gymnosperm female reproductive structures, the carpels (but not necessarily ovules) and female cones, respectively, exhibit a lack of B-like gene expression. One theory that remains relatively untested is that a related lineage, known as Bsister genes, is required for female reproductive identity in angiosperms and gymnosperms. However, based on current data, it is difficult to make generalizations about the evolutionary and developmental role of B-like genes in seed plants. By studying the evolutionary history of B-like genes and Bsister genes in diverse gymnosperms, I am hoping to elucidate the evolutionary relationships of the putative reproductive identity genes in extant seed plants from the most recent common ancestor. This research will establish a broader comparative framework that will advance the study of the evolution and development of seed plant reproductive structures and enable us to address questions of homology and the evolution of diverse reproductive structures in extant gymnosperms.